1. Field of the Invention
The present invent ion relates to an optical fiber module capable of increasing optical coupling efficiency.
2. Description of the Related Art
In an optical fiber communication system, optical sub-assembly for transceivers is an important medium for conversion between optical signals and electrical signals. The optical sub-assembly for transceivers can be classified into transmitting optical sub-assembly (TOSA) for transmitting optical signals, bi-direction optical sub-assembly (BOSA) capable of receiving bi-direction signals in the same optical fiber and tri-direction optical sub-assembly (TRI-DI OSA) capable of receiving both digital signals and analog signals and transmitting digital signals. Either of the TOSA, BOSA and TRI-DI OSA is connected with an optical fiber module 10. Referring to FIG. 1A, the optical fiber module 10 includes a fiber stub structure 11 and an optical transmission line 12 coaxially disposed in the fiber stub structure 11. In general, the optical alignment between the TOSA, BOSA or TRI-DI OSA and the optical fiber module 10 necessitates an X-Y-Z precision positioning stage for performing optical coupling alignment between the optical fiber 13 of the optical transmission line 12 and the light-emitting element of the TOSA, BOSA or TRI-DI OSA so as to transmit optical signals.
The fiber stub structure 11 includes a sleeve 14 and a ferrule 15 coaxially disposed in the sleeve 14 and positioned at a bottom end thereof. The optical fiber 13 partially lengthwise extends into the ferrule 15. The bottom face of the ferrule 15 is an inclined face 16 for preventing reflection light from being incident on the light-emitting element so as to avoid interference of noises with the light-emitting element 17.
Referring to FIG. 1B, as to geometrical optics, the calculation formula of angle of emergence of light beam is as follows:n SIN(θ1)=SIN(θ1+θ2),wherein:n: refractive index of optical fiber;θ1: grinding angle of optical fiber on the end face of the fiber stub; andθ2: angle contained between the axis of optical fiber and the direction of emergence of the light.
In the above arrangement, the ferrule 15 is disposed in the sleeve 14 in an upright state. In this case, according to the above formula, the direction of incidence of optical signal of the light-emitting element 17 is collinear with the optical fiber 13 rather than coaxial with the direction of emergence of the light of the optical fiber 13. Therefore, according to the theory that an optimal path is achieved when the direction of incidence of light and the direction of emergence of light, (that is, angle of incidence of light and angle of emergence of light), are coaxial with each other, this will cause loss to incident optical signal and needs to be overcome.